The relative importance of alternative pathways of methionine metabolism continues to be investigated by use of the rat liver hepatocyte system. This comparison is made by investigating the oxidation rate of the methyl carbon of methionine and Ado-Met at varying concentrations of methionine and Ado-Met along with varying concentrations of glycine and L-serine. Studies on the development pattern of the catabolism of 3-methylthiopropionate in the rat are being continued by investigating the rate of conversion of the methyl carbon of 3-methylthiopropionate to methanthiol and carbon dioxide at varying concentrations of the substrate. Additional studies similar to those discussed above are to be carried out with carboxly labeled 3-methylthiopropionate. One of the major problems to date has been the varying yields of 3-methylthiopropionate obtained from methionine by use of the ninhydrin-aldehyde dehydrogenase system described by us for the synthesis of 3-methylthiopropionate. Thus, a new system for the synthesis of 3-methylthiopropionate from methyl-bromide thiourea and methyl acrylate is being developed. This will allow us to develop specifically labeled 3-methylthiopropionate which can be used in later studies for identification of the products derived from the metabolism of 3-methylthiopropionate. The initial cleavage of 3-methylthiopropionate to methanthiol and other products will be investigated. The subcellular localization and identification of the enzyme(s) responsible for this cleavage will be investigated. It is anticipated that cystathionase or an enzyme with similar specificity is involved.